Synthesis of antimicrobial silsesquioxane-silica hybrids

ABSTRACT

One-pot synthetic methods are disclosed for synthesizing curable, antimicrobial silsesquioxane-silica hybrids by hydrolytically co-condensing a tetraalkoxysilane with two different trialkoxysilanes. Particles are also disclosed that are substantially spherical and have an ordered lamellar internal structure. In addition, polymers prepared front the curable, antimicrobial silsesquioxane-silica hybrids and co-monomers are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/241,078, filed Jan. 7, 2019 (now U.S. Pat. No. 10,995,181), which isa continuation of U.S. application Ser. No. 14/907,799, filed Jan. 26,2016 (now U.S. Pat. No. 10,189,954), which is a U.S. National PhaseApplication of International Application No. PCT/US2014/051243, filedAug. 15, 2014, which claims priority to U.S. Provisional Application No.61/959,177, filed Aug. 16, 2013, each of which are hereby incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to methods of preparingsilsesquioxane-silica hybrids. More particularly, it relates, interalia, to one-pot synthetic methods are disclosed for synthesizingcurable, antimicrobial silsesquioxane-silica hybrids and particlescontaining such hybrids.

BACKGROUND OF THE INVENTION

Organically-modified silicates are organic-inorganic hybrid materials inwhich the organic moieties are covalently linked to the siloxanebackbone (L. Nicole, L. Rozes, C. Sanchez, Adv. Mater., 2010, 22, 3208).Their rheological behavior may be modified by varying the precursorratios, resulting in materials exhibiting rubbery or brittlecharacteristics (J. D. Mackenzie, Y. J. Chung, Y. Hu, J. Non-Cryst.Solids, 1992, 147-148, 271). Silsesquioxanes ([RSiO_(1.5)]_(n)) arespecific examples of organically-modified silicates in which R ishydrogen or any organic group (e.g., alkyl, alkylene, aryl, etc.).Silsesquioxanes or silsesquioxane-silica hybrids are synthesized using aStöber-like sol-gel route (W. Stöber, A. Fink, E. Bohn, J. ColloidInterface Sci., 1968, 26, 62), via hydrolytic condensation oftrialkoxysilanes, bridged alkoxides or co-condensation between atetra-alkoxysilane and a trialkoxysilane (F. Hoffmann, M. Cornelius, J.Morell, M. Fröba, Angew. Chem. Int. Ed., 2006, 45, 3216; H. Mori, Y.Miyamura, T. Endo, Langmuir, 2007, 23, 9014; E. Ruiz-Hitzky, P. Aranda,M. Darder, M. Ogawa, Chem. Soc. Rev., 2011, 40, 801). By controlling theorganic-inorganic composition, as well as functionality of these hybridmaterials, a wide variety of silicate-based hybrid materials may beproduced for applications in the fields of catalysis (F. Hoffmann, M.Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed., 2006, 45, 3216),optical devices (C. Sanchez, B. Lebeau, F. Chaput, J. P. Boilot, Adv.Mater., 2003, 15, 1969), coating and polymer science (X. X. Zhang, B. B.Xia, H. P. Ye, Y. L. Zhang, B. Zhao, L. H. Yan, H. B. Lv, B. Jiang, J.Mater. Chem., 2012, 22, 13132; B. M. Novak, Adv. Mater., 1993, 5, 422).

The introduction of reactive functionalities to silsesquioxanes may beachieved via post-synthetic surface functionalization procedures(grafting), which are based upon chemical reaction of silica particleswith coupling agents bearing organic functional groups. However, thelimitations of the grafting method are that there are relatively fewsilanol groups available on the surface of the silica particles and theprocedure is time-consuming. In addition, this method generally resultsin particles containing only one type of functional group.

Recently, efforts have been made to explore the ability of organosilaneswith surfactant chain-bearing groups to self-direct the hydrolysis andcondensation of alkoxysilane precursors into structures with mesoporouscharacteristics (G. Büchel, K. Klaus, K. K. Unger, A. Matsumoto, K.Tsutsumi, Adv. Mater., 1998, 10, 1036; E. Ruiz-Hitzky, S. Letaïef, V.Prévot, Adv. Mater., 2002, 14, 439; Y. Fujimoto, A. Shimojima, K.Kuroda, J. Mater. Chem., 2006, 16, 986; M. Choi, H. S. Cho, R.Sricastava, C. Venkatesan, D. H. Choi, R. Ryoo, Nat. Mater., 2006, 5,718). Although the mechanisms of using surfactant silanes to facilitateformation of particles with tailored mesostructures (i.e., mesoporous,lamellar, and worm-like mesostrucutures) were well understood, little isknown regarding the synthesis of mesostructured hybrid materials withdual functionalities.

Accordingly, there is a need for methods of preparingsilsesquioxane-silica hybrids and for preparing particles containingthese hybrids having mesoporous characteristics. The methods andcompositions of the present invention are directed toward these, as wellas other, important ends.

SUMMARY OF THE INVENTION

Direct synthesis, in which silica-based hybrid particles are generatedby co-condensation of tetra-alkoxysilane with terminal trialkoxysilane,represents a more advantageous route, with the organic functionalitydistributed within the synthesized materials instead of the surface ofthe materials (A. Van Blaaderen, A. Vrij, J. Colloid Interface Sci.,1993, 156, 1; C. R. Silva, C. Airoldi, J Colloid Interface Sci., 1997,195, 381; S. Chen, S. Hayakawa, Y. Shirosaka, E. Fujii, K. Kawabata, K.Tsuru, A. Osaka, J. Am. Ceram. Soc., 2009, 92, 2074; Y. Naka, Y. Komori,H. Yashitake, Colloids Surf. A. Physicochem. Eng. Aspects, 2010, 36,162). In addition, the organic functionalities are more homogeneouslydistributed during the co-condensation process, when compared withmaterials that are produced by the grafting method. This is especiallyso in the case of fabricating mesoporous structures in which organicfunctionalization of the center of the pores through grafting method maybe impaired as a result of the pore blocking effect if the organosilanesreact preferentially at pore openings. It is generally believed thatperiodic mesoporous organsilica particulates that are produced viahydrolysis and condensation reactions of bridged organosilica precursorshave a higher degree of homogeneity of the organic functionalities (F.Hoffmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed.,2006, 45, 3216). Despite ample reports of such a method, the literatureis sparse in the synthesis of silica-based hybrids containing dualfunctional groups.

A modified Stöber route for synthesizing silsesquioxane-silica hybrid(SqSH) particles by hydrolytic co-condensation of tetraethoxysilane(TEOS) with two trialkoxysilanes:3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (SiQAC) and3-methacryloxypropyltrimethoxysilane (3-MPTS), in one embodiment,without the use of an additional surfactant. The alkylammonium chainfrom SiQAC is responsible for its antimicrobial potential (Ahlström B.,Thompson R. A., Edebo L., APMIS, 1999, 107, 318), and serves as astructure-directing agent (i.e., surfactant silane) during theco-condensation process Q. Huo, D. I. Margolese, G. D. Stucky, Chem.Mater., 1996, 8, 1147). The dual roles of SiQAC as a surfactant silaneand the contributor of the antimicrobial functionality eliminates theneed for surfactant removal after synthesis, thereby avoiding the riskof destroying the other organic functionality (i.e., methacrylate groupsfrom 3-MPTS, for example in one embodiment) during removal of surfactantby extractive or calcination methods. In this one-pot synthesis, themolar ratio of SiQAC and 3-MPTS was maintained at 1:1, while the molarratio of TEOS varied from 1 to 32, resulting in silsesquioxane-silicahybrids (SqSHs) with overall molar ratios of 1:1:1, 1:2:1, 1:4:1, 1:8:1,1:16:1 and 1:32:1. The sol-gel hydrolytic condensation product of TEOSwas used as a comparative example (sol-gel silica).

Accordingly, in a first embodiment, the invention is directed to methodsof preparing a silsesquioxane-silica hybrid, comprising:

hydrolytically co-condensing, in the presence of at least one(C₁-C₃)alcohol and a catalytic amount of an ammonium cation (NH₄ ⁺), ofa tetralkoxysilane of formula I:

with a trialkoxysilane of formula II:

and with a trialkoxysilane of formula III:

wherein said compound of formula II, said compound of formula I, andsaid compound of formula III are reacted in a molar ratio of about1:1-32:1, respectively;

wherein:

-   -   A¹, A², A³, and A⁴ are each independently selected from the        group consisting of H, C₁-C₈alkyl, and trifluoro-substituted        (C₁-C₈)alkyl;    -   R³ is independently a functional group comprising at least one        curing group selected from the group consisting of acrylate,        methacrylate, (C₂-C₈)alkenyl, glycidyloxy, epoxy, sulfonate,        carboxylate, ester, amino, acrylamide, methacrylamide,        isocyanato, amino acid, nucleic acid, and mercapto(C₁-C₆)alkyl;    -   R^(b) is independently

-   -   -   wherein:        -   R^(c) is (C₁-C₂)alkyl;        -   R^(d) is (C₁-C₂)alkyl or phenyl;        -   R^(e) is (C₆-C₂₂)alkyl;        -   X⁻ is an anion selected from the group consisting of            chloride, bromide, fluoride, iodide, sulfonate, and acetate;

each R^(y) is, independently, H, (C₁-C₈)alkyl, or trifluoro-substituted(C₁-C₈)alkyl.

In other embodiments, the invention is directed to the particlesproduced by the process. In certain embodiments, these particles have asubstantially spherical morphology. In certain embodiments, theseparticles have a substantially ordered lamellar internal structure. Incertain embodiments, these particles are mesoporous. In certainembodiments, these particles have the reacted residue of saidtrialkoxysilane of formula II and the reacted residue of saidtrialkoxysilane of formula III are substantially homogeneouslydistributed throughout said particle.

Other embodiments are directed to a plurality of particles, wherein eachof said particles comprises:

a silsesquioxane-silica hybrid;

wherein each of said particles has a substantially spherical morphology;

wherein each of said particle has a substantially ordered lamellarinternal structure;

wherein each of said particle is mesoporous; and

wherein the reacted residue of said trialkoxysilane of formula II andthe reacted residue of said trialkoxysilane of formula III aresubstantially homogeneously distributed throughout each of saidparticle.

In yet other embodiments, the invention is directed to methods ofpreparing a polymer, comprising:

providing a plurality of particles described herein;

substantially fully hydrolyzing said particles to form a plurality ofhydrolyzed particles; and

reacting said plurality of hydrolyzed particles with at least oneco-monomer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 shows a one-pot, co-condensation reaction scheme of oneembodiment of the method of the invention.

FIGS. 2 a to 2 d show ²⁹Si cross polarization-magic angle spinningnuclear magnetic resonance spectroscopy (CP-MAS NMR).

FIG. 2 e shows the Fourier transform infrared spectroscopy (FTIR) ofsilsesquioxane-silica hybrids (SqSHs) of one embodiment of the inventionand a comparative sol-gel silica. The broad absorbance band from˜1000-1100 cm⁻¹ is assigned to asymmetric stretching vibration ofSi—O—Si groups. With higher organic content in the hybrid (SqSH 1:1:1and SqSH 1:2:1), two separate peaks are present, indicating twocomponents from Si—O—Si groups in cyclic (˜1080 cm⁻¹) and linear (˜1040cm⁻¹) structures. Cyclic structure of Si—O—Si is considered to be morecondensed than linear Si—O—Si. This is consistent to ²⁹Si NMR resultsshowing that SqSH 1:1:1 and SqSH 1:2:1 have higher degrees ofcondensation (FIG. 2 d ). The peaks at ˜792 cm⁻¹ and ˜430 cm⁻¹ areassigned to Si—O—Si bending and rock vibration, respectively. The peakat ˜935 cm⁻¹ is derived from silanol group (SiOH). The absorbance bandpeaking at 1633 cm⁻¹ is assigned to deformational vibration of absorbedwater molecules (Si—H₂O). The presence of methacrylate from 3-MPTS areconfirmed by peaks at 1690-1714 cm⁻¹ (C═O), 1637 cm⁻¹ (C═C), 1305 cm⁻¹(C—CO—O), 1295 cm⁻¹ (C—CO—O), and 815 cm⁻¹ (C═C). The C—N stretchvibration peaking at 1373 cm⁻¹ validates the presence of SiQAC.

FIG. 3 shows small-angle powder X-ray diffraction (XRD) patterns of theSqSH 1:n:1 hybrids (n=2, 8, 16, 32)

FIGS. 4 a to f show electron micrographs.

FIGS. 5 a to c show thermogravimetric analysis (TGA) of one embodimentof the invention and a comparative sol-gel silica at a rate of 10°C./min from ambient temperature to 1000° C. in atmospheric air. (a)Thermograms for SqSHs and sol-gel silica. The residual mass that remainsafter reaching at 700° C. is due to residual inorganic silica content.The weight percentage of remaining silica in SqSHs 1:1:1, 1:2:1, 1:4:1,1:8:1, 1:16:1, 1:32:1 and comparative sol-gel silica are 22.7, 31.3,38.7, 50.1, 58.7, 68.8, and 76.7 weight %, respectively. (b) Logarithmicregression model provides an excellent fit (R²=0.987; P<0.01) for therelation between the residual weight percentage and the molar ratio oftetraethoxysilane to a trialkoxysilane. (c) Derivative weight losscurves for SqSHs and sol-gel silica. For the peak below 100° C. (A), thehighest was seen with sol-gel silica while the lowest peak was seen withSqSH 1:1:1. This indicates that there is more water molecules inside thesol-gel silica network. The overall peak intensity of the derivativeweight plots increases with the increased composition of organosilane inSqSHs. The two peaks (B and C) from 200 to 420° C. indicate thedecomposition of organic constituents (D. S. Bag, K. U. Rao, J. Appl.Poly. Sci. 2010, 115, 2352), representing two-stage decomposition oforganic substances from SqSHs (W. Xie, Z. Gao, W.-P. Pan, D. Hunter, A.Singh, R. Vaia, Chem. Mater. 2001, 13, 2979). The peaks (D) above 600°C. are attributed to further condensation of the silanol groups in thebulk silicate network.

FIG. 6 shows partial coalescence of SqSHs of one embodiment of theinvention to form peanut-like structures. Unstained transmissionelectron microscopy image of the formation of partially coalesced,peanut-like particles derived from SqSH 1:4:1. This clumping phenomenonis observed in all SqSH versions with different feed ratios, but not forthe sol-gel silica control. The process should have occurred while theSIQAC- and ethanol-stabilized droplets are in their liquid phase priorto solidification. It is possible that the quaternary ammoniumtrialkoxysilane (SiQAC) located on the surface of droplets with longhydrophobic alkyl chain protrudes from a lipophilic droplet into thecontinuous aqueous phase. Upon collision with another globule, thesealkyl chains may pierce the other globule, making the droplets moreprone to partial coalescence (E. Fredrick, P. Walstra, K. Dewettinck,Adv. Colloid Interface Sci. 2010, 153, 30). Scale bar=100 nm.

FIGS. 7 a to 7 d show mechanical testing (modulus and hardness).

FIGS. 8 a to 8 c shows antimicrobial potentials with XTT and CFU assaysagainst (a) S. mutans; (b) A. naeslundii; and (c) C. albicans.

FIG. 9 a shows scanning transmission electron microscopy energydispersive X-ray analysis (STEM-EDX) mappings of distribution of carbon,nitrogen, oxygen, and silicon within SqSH (at molar ratio 1:8:1) of oneembodiment of the invention. FIG. 9 b shows scanning transmissionelectron microscopy-energy dispersive X-ray analysis (STEM-EDX) mappingsof distribution of carbon, nitrogen, oxygen, and silicon within SqSH (atmolar ratio 1:32:1) of another embodiment of the invention.

FIGS. 10A and 10B show cytotoxicity of one embodiment of the inventionand a comparative sol-gel silica. FIG. 10A depicts mitochondrialsuccinic dehydrogenase activities of L-929 cells after incubating for 72hours in DMEM containing SqSH or silica particles at differentconcentrations. Cytotoxicity of the SqSH particles on mammalian cellsincreased in a dose dependent manner. FIG. 10B depicts the concentrationof different SqSH versions leading to 50% reduction in cell viability(IC₅₀) of the L-929 cells is illustrated here. IC₅₀ was determined byplotting the logarithm of particle concentration vs. reduction in cellviability. Note that sol-gel silica particles (predominantly inorganicin nature) are highly biocompatible and did not result in loss of cellviability reduction. A linear regression model was used to describe therelationship (R²=0.982; P<0.05) between the IC₅₀ and the molar ratio oftetraethoxysilane to a trialkoxysilane.

DETAILED DESCRIPTION OF THE INVENTION

As employed above and throughout the disclosure, the following terms,unless otherwise indicated, shall be understood to have the followingmeanings.

As used herein, the singular forms “a,” “an,” and “the” include theplural reference unless the context dearly indicates otherwise.

“Alkyl,” as used herein, refers to an optionally substituted, saturatedstraight, branched, or cyclic hydrocarbon having from about 1 to about20 carbon atoms (and all combinations and subcombinations of ranges andspecific numbers of carbon atoms therein), with from about 1 to about 8carbon atoms or 1 to 6 carbon atoms (C₁-C₆) being preferred, and withfrom about 1 to about 4 carbon atoms. Alkyl groups include, but are notlimited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,t-butyl, n-pentyl, cyclopentyl, cyclopropyl, isopentyl, neopentyl,n-hexyl, isohexyl, cyclohexyl, cyclooctyl, adamantyl, 3-methylpentyl,2,2-dimethylbutyl, and 2,3-dimethylbutyl. A branched alkyl group has atleast 3 carbon atoms (e.g., an isopropyl group), and in variousembodiments, has up to 6 carbon atoms, i.e., a branched lower alkylgroup. A branched alkyl group has at least 3 carbon atoms (e.g., anisopropyl group), and in various embodiments, has up to 6 carbon atoms,i.e., a branched lower alkyl group.

“Alkenyl,” as used herein, refers to an optionally substituted, singlyunsaturated, straight, branched, or cyclic hydrocarbon having from about2 to about 20 carbon atoms (and all combinations and subcombinations ofranges and specific numbers of carbon atoms therein), with from about 2to about 8 carbon atoms or 2 to 6 carbon atoms (C₂-C₆) being preferred.Alkenyl groups include, but are not limited to, ethenyl (or vinyl),allyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, and octenyl.

“Alkylenyl,” as used herein, refer to the subsets of alkyl groups, asdefined herein, including the same residues as alkyl but having twopoints of attachment within a chemical structure. Examples of(C₁-C₆)alkylenyl include methylenyl (—CH₂—), ethylenyl (—CH₂CH₂—),propylenyl (—CH₂CH₂CH₂—), and dimethylpropylenyl (—CH₂C(CH₃)₂CH₂—).

“Aryl,” as used herein, refers to an optionally substituted, mono-, di-,tri-, or other multicyclic aromatic ring system having from about 5 toabout 50 carbon atoms (and all combinations and subcombinations ofranges and specific numbers of carbon atoms therein), with from about 6to about 10 carbons (C₆-C₁₀) being preferred. Non-limiting examplesinclude, for example, phenyl, naphthyl, anthracenyl, and phenanthrenyl.

As used herein, the terms “optionally substituted” or “substituted orunsubstituted” are intended to refer to the optional replacement of upto four hydrogen atoms with up to four independently selectedsubstituent groups as defined herein. Unless otherwise specified,suitable substituent groups independently include hydroxyl, nitro,amino, imino, cyano, halo, thio, sulfonyl, aminocarbonyl, carbonylamino,carbonyl, oxo, guanidine, carboxyl, formyl, alkyl, perfluoroalkyl,alkylamino, dialkylamino, alkoxy, alkoxyalkyl, alkylcarbonyl,arylcarbonyl, alkylthio, aryl, heteroaryl, a heterocyclic ring,cycloalkyl, hydroxyalkyl, carboxyalkyl, haloalkyl, alkenyl, alkynyl,arylalkyl, aryloxy, heteroaryloxy, heteroarylalkyl, and the like.Substituent groups that have one or more available hydrogen atoms can inturn optionally bear further independently selected substituents, to amaximum of three levels of substitutions. For example, the term“optionally substituted alkyl” is intended to mean an alkyl group thatcan optionally have up to four of its hydrogen atoms replaced withsubstituent groups as defined above (i.e., a first level ofsubstitution), wherein each of the substituent groups attached to thealkyl group can optionally have up to four of its hydrogen atomsreplaced by substituent groups as defined above (i.e., a second level ofsubstitution), and each of the substituent groups of the second level ofsubstitution can optionally have up to four of its hydrogen atomsreplaced by substituent groups as defined above (i.e., a third level ofsubstitution).

“Mesoporous,” as used herein, refers to a material containing pores withdiameters about 2 nm to about 50 nm.

“Polydispersity index,” as used herein, refers to the ratio ofweight-average molecular weight to the number-average molecular weight(PDI=M_(w)/M_(n)).

“Molecular weight,” as used herein, unless otherwise indicated, refersto the weight average molecular weight of a polymer as measured by gelpermeation chromatography (GPC) against a polyacrylic acid standard.

While the present invention is capable of being embodied in variousforms, the description below of several embodiments is made with theunderstanding that the present disclosure is to be considered as anexemplification of the invention, and is not intended to limit theinvention to the specific embodiments illustrated. Headings are providedfor convenience only and are not to be construed to limit the inventionin any manner. Embodiments illustrated under any heading may be combinedwith embodiments illustrated under any other heading.

The use of numerical values in the various quantitative values specifiedin this application, unless expressly indicated otherwise, are stated asapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations from a stated value can be used to achievesubstantially the same results as the stated value. Also, the disclosureof ranges is intended as a continuous range including every valuebetween the minimum and maximum values recited as well as any rangesthat can be formed by such values. Also disclosed herein are any and allratios (and ranges of any such ratios) that can be formed by dividing arecited numeric value into any other recited numeric value. Accordingly,the skilled person will appreciate that many such ratios, ranges, andranges of ratios can be unambiguously derived from the numerical valuespresented herein and in all instances such ratios, ranges, and ranges ofratios represent various embodiments of the present invention.

As used herein, the phrase “substantially” means have no more than about10% difference between the target and actual level, preferably less thanabout 5% difference, more preferably, less than about 1% difference.

We have developed a facile method for synthesizing unique SqSH hybridsilica particles via a Stöber-like approach, with ordered lamellarstructures with spherical morphology, without the use of additionalsurfactants. A scheme illustrating the influence of surfactant andformation of SqSH-silica hybrid nanospheres is shown in FIG. 1 . Thisone-pot synthesis approach leads to the development of unique and usefulantimicrobial hybrid silica particles with quaternary ammonium groupsdistributed within the entire particles, and therefore, non-leachingantimicrobial activities, as opposed to a grafting procedure, where thustype of functionality is present only along the particle surface.Moreover, antimicrobial activities are present irrespective of thedegree of mesoscopic order of the hybrid silica particles. Thissynthesis approach may be further expanded by replacing the methacrylatefunctionality with other organofunctional moieties, thereby enabling theantimicrobial hybrid particles with tunable mechanical properties to beincorporated into different polymers/copolymers for a wide range ofcommercial applications. Likewise, this synthesis approach may befurther expanded by replacing the antimicrobial functionality with otherorganofunctional moieties, thereby enabling the antimicrobial hybridparticles with tunable biological properties to be incorporated intodifferent polymers/copolymers for a wide range of commercialapplications.

Accordingly, in a first embodiment, the invention is directed to methodsof preparing a silsesquioxane hybrids comprising:

hydrolytically co-condensing, in the presence of at least one(C₁-C₃)alcohol and a catalytic amount of an ammonium cation (NH₄ ⁺), ofa tetralkoxysilane of formula I:

with a trialkoxysilane of formula II:

and with a trialkoxysilane of formula III:

wherein said compound of formula II, said compound of formula I, andsaid compound of formula III are reacted in a molar ratio of about1:1-32:1, respectively;

wherein:

A¹, A², A³, and A⁴ are each independently selected from the groupconsisting of H, C₁-C₈alkyl, and trifluoro-substituted (C₁-C₈)alkyl;

R^(a) is independently a functional group comprising at least one curinggroup selected from the group consisting of acrylate, methacrylate,(C₂-C₈)alkenyl, glycidyloxy, epoxy, sulfonate, carboxylate, ester,amino, acrylamide, methacrylamide, isocyanato, amino acid, nucleic acid,and mercapto(C₁-C₆)alkyl;

R^(b) is independently

-   -   wherein:    -   R^(c) is (C₁-C₂)alkyl;    -   R^(d) is (C₁-C₂)alkyl or phenyl;    -   R^(e) is (C₆-C₂₂)alkyl;    -   X⁻ is an anion selected from the group consisting of chloride,        bromide, fluoride, iodide, sulfonate, and acetate;

each R^(y) is, independently, H, (C₁-C₈)alkyl, or trifluoro-substituted(C₁-C₈)alkyl. The silsesquioxane-silica hybrid compounds that are formedmay be linear, branched, or star-shaped with the residues of compound Iforming the backbone and the residues of compounds of formula II andformula III terminally located on the compounds.

In certain embodiments, said (C₁-C₃)alcohol is methanol, ethanol,propanol (n-propanol or isopropanol), or mixtures thereof. In certainembodiments, the (C₁-C₃)alcohol is ethanol.

In certain embodiments, said ammonium cation (NH₄ ⁺) is derived fromammonium hydroxide, ammonium carbonate, ammonium chloride, ammoniumnitrate, aqueous ammonia, or a mixture thereof. In certain embodiments,said ammonium cation (NH₄ ⁺) is derived from ammonium hydroxide.

In certain embodiments, each R^(y) is, independently, R^(y) is,independently, H, methyl, ethyl, or propyl. In certain embodiments, eachR^(y) is H. In certain embodiments, each R^(y) is methyl.

In certain embodiments, said siloxane of formula I istetra(C₁-C₆)alkoxysilane. In certain embodiments, said siloxane offormula I is tetramethoxysilane (TMOS), tetraethoxysilane (TEOS),tetrapropoxysilane (TPOS), or a mixture thereof. In certain embodiments,said siloxane of formula I is tetraethoxysilane (TEOS).

In certain embodiments, R^(a) is acrylate, methacrylate, or vinyl,preferably methacrylate. In certain embodiments, R^(a) ismethacryloxypropyl.

In certain embodiments, said trialkoxysilane of formula II is3-methacryloxypropyl trimethoxysilane (3-MPTS).

In certain embodiments, R^(y) is H or (C₁-C₂)alkyl. Ethyl is preferredfor certain dental and medical applications. In certain embodiments,R^(y) is H.

In certain embodiments, R^(b) is independently —(C₃-C₆alkylenyl)-(dimethyl)-(C₆-C₂₂alkyl) quaternary ammonium chloride or—(C₃-C₆ alkylenyl)-(methyl)-(phenyl)-(C₆-C₂₂alkyl) quaternary ammoniumchloride. In certain embodiments, R^(b) is—(C₃-C₆)alkylenyl-dimethyl-(C₁₈alkyl) quaternary ammonium chloride,especially R^(b) is —(C₃ alkylenyl)-(dimethyl)-(C₁₈alkyl) quaternaryammonium chloride, such Aegis 5700 or 5772 commercially available fromAegis or R^(b) is —(C₃-C₆)alkylenyl-methyl-phenyl-(C₆-C₂₂alkyl)quaternary ammonium chloride, which may be prepared by N-alkylation ofN-hexylaniline in a two-step process where N-hexylanlysis is reactedwith 3-chloropropyl)triethoxysilane to yield a tertiary amine which thenis further quarternized in the second step by reacting with iodomethane,such as described in Saif, et al., Langmuir, 2009, 25, 377-379.

In certain embodiments, R^(b) is

In certain embodiments, R^(c) is methyl.

In certain embodiments, R^(d) is methyl.

In certain embodiments, R^(e) is octadecyl.

In certain embodiments, X^(⊖) is Cl⁻.

In certain embodiments, said trialkoxysilane of formula III is3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (SiQAC).

In certain embodiments, said method is conducted substantially free of aseparate surfactant other than said compound of formula II.

In certain embodiments, said compound of formula II, said compound offormula I, and said compound of formula III are reacted in a molar ratioselected from the group consisting of 1:1:1, 1:2:1, 1:4:1, 1:8:1,1:16:1, 1:32:1, and mixtures thereof, respectively.

In other embodiments, the invention is directed to the particlesproduced by the process. In certain embodiments, these particles have asubstantially spherical morphology. In certain embodiments, theseparticles have a substantially ordered lamellar internal structure. Incertain embodiments, these particles are mesoporous. In certainembodiments, these particles have the reacted residue of saidtrialkoxysilane of formula II and the reacted residue of saidtrialkoxysilane of formula III are substantially homogeneouslydistributed throughout said particle.

Other embodiments are directed to a plurality of particles, wherein eachof said particles comprises:

a silsesquioxane-silica hybrid;

wherein each of said particles has a substantially spherical morphology;

wherein each of said particle has a substantially ordered lamellarinternal structure;

wherein each of said particle is mesoporous; and

wherein the reacted residue of said trialkoxysilane of formula II andthe reacted residue of said trialkoxysilane of formula III aresubstantially homogeneously distributed throughout each of saidparticle.

In certain embodiments, said plurality of particles has an averageparticle size of about 50 nm to about 2000 nm, preferably about 250 nmto about 1000 nm. In certain embodiments, said plurality of particleshas a polydispersity index of about 1 to about 20. In certainembodiments, the M_(w) is about 20,000 to about 200,000.

In yet other embodiments, the invention is directed to methods ofpreparing a polymer, comprising:

providing a plurality of particles described herein;

substantially fully hydrolyzing said particles to form a plurality ofhydrolyzed particles; and

reacting said plurality of hydrolyzed particles with at least oneco-monomer.

In another embodiment, the invention is directed to kits, comprising:

a plurality of particles described herein;

at least one polymerization initiator;

optionally, at least one synergist;

optionally, at least one filler; and

optionally, at least one co-monomer.

In other embodiments, the invention is directed to compositions,comprising:

at least one filler;

a plurality of particles described herein;

-   -   wherein said plurality of particles is sorbed on said filler.

In other embodiments, the compositions, further comprise:

at least one natural rubber, synthetic rubber, or a combination thereof.

In another embodiment, the compositions, further comprise:

at least one first polymer selected from the group consisting ofthermoplastic polymer, thermosetting polymer, and mixtures thereof.

In yet other embodiments, the invention is directed to polymericarticles, comprising:

said compositions described herein, said particles described herein or apolymerized residue of said particles described herein.

In further embodiments, the invention is directed to coating materials,comprising:

said compositions described herein, said particles described herein or apolymerized residue of said particles described herein.

In other embodiments, the invention is directed to compositionscomprising:

the polymerized residue of said particles described herein.

In another embodiment, the invention is directed to toothpastes,comprising:

said compositions described herein or said particles described herein.

In other embodiments, the invention is directed to mouthwashes,

comprising:

said compositions described herein or said particles described herein.

In yet other embodiments, the invention is directed to contact lenses,comprising:

said compositions described herein, said particles described herein or apolymerized residue of said particles described herein.

In other embodiments, the invention is directed to the products producedby the processes and methods described herein.

Another embodiment of this invention is a water solution of saidcompositions described herein, said particles described herein or apolymerized residue of said particles described herein.

Still another embodiment of this invention is a water-alcohol solutionof said compositions described herein, said particles described hereinor a polymerized residue of said particles described herein.

Yet another embodiment is the use of the material described herein asfillers for adhesive (primer) and the use of the material describedherein in commercial adhesives used in dentistry.

Still another embodiment is the use of a material described herein as anadditive (filler) to dental compositions for adhesion of the dentalcomposition to a tooth. Other embodiments include the use of a materialdescribed herein as fillers for plastic bags, polyethylene films,toothpastes, and any other application requiring a filler polymer,especially one that is antimicrobial.

In addition, the materials of this invention can act as toothdesensitizers when placed on a tooth, and still further, this materialcan be added to filler material for teeth, especially filling materialssuch as siloxanes, glass ionomers, methacrylates, and silver amalgams.

In still other embodiments, the materials of the invention may be usedin contact lenses as the primary material or as a secondary material.

In certain embodiments, the compositions described herein furthercomprise at least one natural rubber, synthetic rubber, or a combinationthereof. In certain other embodiments, the compositions further compriseat least one first polymer selected from the group consisting ofthermoplastic polymer, thermosetting polymer, and mixtures thereof.

In certain embodiments, the compositions comprising said compositionsdescribed herein, said particles described herein or a polymerizedresidue of said particles described herein, further comprise at leastone first polymer selected from the group consisting of thermoplasticpolymer, thermosetting polymer, and mixtures thereof.

Suitable thermoplastic polymers for use in the compositions of theinvention include, but are not limited to, polyethylene, polypropylene,polyvinyl chloride, polyester, acrylic, methacrylic, or a copolymer ormixture thereof.

Suitable thermosetting polymers for use in the compositions of theinvention include, but are not limited to, epoxy, polyester, alkyd,diallyl phthalate, melamine, polybutadiene, phenolic, silicone, urea,urethane, imide, or a mixture thereof.

In certain embodiments, the compositions described herein, the particlesdescribed herein or a polymerized residue of the particles describedherein are in the form of a powder. In certain embodiments, thecompositions of the invention are in the form of a master batch. A“master batch,” as used herein, is a product in which additives aredispersed (usually well dispersed) in a carrier material that iscompatible with the main polymer or plastic in which it will be let downand may be supplied in a granule, a pellet, or a powder form. In certainembodiments, the compositions of the invention further comprise a secondpolymer that is the same or different from the first polymer.

In certain embodiments, the compositions described herein, the particlesdescribed herein or a polymerized residue of the particles describedherein, with or without filler, further comprise at least one firstpolymer wherein said first polymer is:

-   -   acrylonitrile-butadiene-styrene;    -   acetal;    -   acrylic;    -   methacrylic;    -   cellulosic (such as acetate, butyrate, ethyl cellulose, nitrate,        propionate);    -   ethylene copolymers (such as ethylene methyl acrylate,        ethylene-n-butyl acrylate, ethylene vinyl acetate, ethylene        methyl acrylic acid, ethylene acrylic acid, ethylene ethyl        acrylate);    -   fluoropolymer (such as fluorinated ethylene propylene,        polytetrafluoroethylene, chlorotrifluoroethylene, polyvinylidene        fluoride, ethylene tetrafluoroethylene-ethylene        chlorotrifluoroethylene);    -   nylon (such as nylon 6/6, 6, 6/10, 8, 12, and copolymers        thereof);    -   polyarylate;    -   polyarylsufone;    -   polybutylene;    -   polycarbonate;    -   polycarbonate-acrylonitrile-butadiene-styrene alloy;    -   polyesters (such as polyethylene terephthalate, polybutylene        terephthalate, polytetramethylene terephthalate, and copolymers        thereof);    -   polyetheretherketone;    -   polyetherimide;    -   polyethersulfone;    -   polyethylene (low density, linear low density, high density,        high molecular weight);    -   ionomer;    -   polymethylpentene;    -   polyphenylene oxide;    -   polyphenylene sulfide;    -   polyimide;    -   polyproplylene (general purpose, impact copolymers, random        copolymers);    -   polystyrene (general purpose, high impact, medium impact);    -   polysulfone;    -   polyurethane;    -   polyvinyl chloride;    -   chlorinated polyvinyl chloride;    -   polyvinyl chloride-acrylic;    -   polyvinyl chloride-acrylonitrile-butadiene-styrene;    -   styrene acrylonitrile;    -   styrene maleic anhydride;    -   thermoplastic elastomer;    -   thermoplastic vulcanizate; or    -   a copolymer or a mixture thereof.

In certain embodiments, the compositions described herein, the particlesdescribed herein or a polymerized residue of the particles describedherein and filler further comprise at least one thermoplastic polymer,thermosetting polymer, or a combination thereof. Suitable thermoplasticpolymers include, but are not limited to, polyethylene, polypropylene,polyvinyl chloride, polyesters, and the like, copolymers and mixturesthereof.

In certain embodiments, the compositions described herein, the particlesdescribed herein or a polymerized residue of the particles describedherein, with or without filler, are useful as polymeric articles, suchas film, sheet, container, foam container, bottle, crate, plastic parts,toys, pipe, foam insulation, panel, plastic lumber, or the like. Incertain embodiments, the polymeric article is prepared by blown film,cast film, extrusion (such as profile extrusion, sheet extrusion, andfoam extrusion), roto-molding, injection molding, blow molding, foamed,coating, or a combination thereof or the like.

In certain embodiments, the compositions described herein, the particlesdescribed herein or a polymerized residue of the particles describedherein, with or without filler, are useful as toothpaste, mouthwash,contact lenses (for example in heat curable systems with HEMA and asmall amount of ethyleneglycol methacrylate), artificial nails andadhesives therefor, and the like.

The compositions described herein, the particles described herein or apolymerized residue of the particles described herein may be used toincrease the contact angle (and hence increase the surface energy) ofcompositions into which they are incorporated. Thus, the compounds ofthe invention are useful in methods of increasing the printabilityand/or dyeability of a polymeric composition. For example, this wouldlead to better print quality and permitting use ofenvironmentally-friendly water-based inks in the place of solvent-basedinks. Such methods comprise incorporating said compositions describedherein, said particles described herein or a polymerized residue of saidparticles described herein into a polymeric composition, either as aseparate component or as a residue in the polymer itself (bypolymerizing with at least one co-monomer).

The compositions described herein, the particles described herein or apolymerized residue of the particles described herein may be used toincrease the hydrophilicity, improve antistatic properties, and reducesurface resistivity (by attracting water) of the compositions into whichthey are incorporated. Such methods comprise incorporating thecompositions described herein, the particles described herein or apolymerized residue of the particles described herein into a polymericcomposition, either as a separate component or as a residue in thepolymer itself (by polymerizing with at least one co-monomer).

The present invention is further defined in the following Examples, inwhich all parts and percentages are by weight, unless otherwise stated.It should be understood that these examples, while indicating preferredembodiments of the invention, are given by way of illustration only andare not to be construed as limiting in any manner. From the abovediscussion and these examples, one skilled in the art can ascertain theessential characteristics of this invention, and without departing fromthe spirit and scope thereof, can make various changes and modificationsof the invention to adapt it to various usages and conditions.

EXAMPLES

Materials and Methods

Chemicals and reagents: Tetraethoxysilane (TEOS),3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (SiQAC),3-methacryloxypropyltrimethoxysilane (3-MPTS), ammonium hydroxidesolution (28-30% NH₃), triethylene glycol dimethacrylate (TEGDMA),ethyl(4-dimethylamino)benzoate (EDMAB) and camphorquinone (CQ) werepurchased from Sigma-Aldrich (St Louis, Minn., USA) and used withoutfurther purification. The SiQAC was supplied at 72 weight % in methanol.2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) wasa gift from Esstech, Inc. (Essington, Pa., USA).

Co-Condensation Procedure

The molar ratio of SiQAC and 3-MPTS was maintained at 1:1, while themolar ratio of TEOS varied from 1 to 32, resulting insilsesquioxane-silica hybrids (SqSHs) with overall molar ratios of1:1:1, 1:2:1, 1:4:1, 1:8:1, 1:16:1 and 1:32:1 (FIG. 1 ). The sol-gelhydrolysis/condensation product of TEOS was used as control (sol-gelsilica). Co-condensation was processed via a modified Stöber route W.Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci., 1968, 26, 62): 16mL of ethanol, 25 mL of deionized water, and 9 mL of NH₄OH solution weremixed and stirred at 1200 rpm. To this solution, 5 mL of TEOS, orSiQAC-3-MPTS-TEOS premixed in 45 mL of ethanol, was rapidly added. After1 minute, the stirring speed was reduced to 350 rpm. The reaction wasmaintained at room temperature for 2 hours. The product was thencentrifuged and washed with copious amounts of water and ethanol. Theprocedures were repeated three times before the reaction products weredried under vacuum. The yield varied from 55 to 86 weight %. The yieldof the SqSHs varied with respect to the molar ratio of thetrialkoxysilane (i.e., high proportion of trialkoxysilane decreased theyield rate). Due to the different hydrolysis and condensation kineticsof the structurally different precursors, a relatively higher proportionof trialkoxysilane in the reaction mixture favors homocondensationreactions of the trialkoxysilanes, at the expense of co-condensationwith the inorganic silica precursor (TEOS). This accounts for the widevariety in yields among the SqSHs prepared with different molar ratiosof the precursors after ethanol extraction of the homocondensationreaction products.

Attenuated total reflection-Fourier transform infrared (FTIR)spectroscopy

Infrared spectra were recorded between 4,000-400 cm⁻¹ using aFourier-transform infrared spectrometer (Nicolet 6700, ThermoScientific, Waltham, Mass., USA) with an attenuated total reflection(ATR) set up at a resolution of 4 cm⁻¹ and averaging 32 scans perspectrum.

Nuclear Magnetic Resonance (NMR) Characterization

The structures of SqSHs and sol-gel silica were characterized by ²⁹Sisolid-state NMR at ambient temperature using a 270 MHz spectrometer(JEOL, Tokyo, Japan) equipped with a 7 mm Magic Angle Spinning (MAS)probe. Spectra were acquired in the ¹H→²⁹Si cross polarization (CP)mode, using a MAS frequency of 4 kHz, with a 45 degree pulse angle of 5psec. The ¹H Larmor frequency for ²⁹Si was 53.76 MHz. Chemical shiftswere referenced to external tetramethylsilane (TMS) at 0 ppm.

Thermogravimetric Analysis (TGA)

TGA was performed with a Q500 thormogravimetric analyzer (TAInstruments, New Castle, Del., USA). Approximately 40 mg of driedparticles (SqSHs or sol-gel silica) was placed in individual platinumpans and heated at a rate of 10° C./min to 1000° C. in atmospheric air.The data were analyzed using the Universal Analysis 2000 software (TAInstruments) and expressed as weight vs temperature as well asderivative weight vs temperature.

Powder X-Ray Diffraction (XRD)

X-ray diffraction (Rigaku America, Woodlands, Tex., USA) of thenon-sintered particles was performed using Ni-filtered Cu Kα radiation(30 KeV, 20 mA), in the 20 range of 1-30°, with a scan rate of 4°/min,and a sampling interval of 0.02°. The determination of d-spacing valueswas based on Bragg-Brentano geometry.

Electron Microscopy

Dried particles sputter-coated with gold/palladium were examined using afield emission-scanning electron microscope (XL-30 FEG; Philips,Eindhoven, The Netherlands) operating at 10-15 kV. Dried particles wereembedded in epoxy resin and cut into 70-90 nm thick sections. Unstainedsections were examined using a JSM-1230 transmission electron microscope(JEOL, Tokyo, Japan) at 110 kV. Selected area electron diffraction(SAED) was performed to identify the crystallinity of the SqSHparticles.

Scanning Transmission Electron Microscopy-Energy Dispersive X-RayAnalysis (STEM-EDX)

Elemental analysis of representative SqSH 1:8:1 and 1:32:1 was performedon unstained thin sections prepared previously for TEM using a Tecnai G2STEM (FEI, Hillsboro, Oreg., USA) at 200 kV. Spectrum acquisition andelemental mapping were conducted using an Oxford Instruments INCAx-sight detector. Images were collected with a Gatan 1K×1K CCD camera.Elemental mappings were acquired with the FEI TIA software using a spotdwell time of 300 msec. As each 250×250 pixel mapping required 7 hoursto complete, drift correction was performed after every 30 images.

Nanoindentation

Cold-polymerized epoxy resin with embedded SqSH or sol-gel silicaparticles was sectioned with a water-cooled diamond-impregnated blasé toexpose the particles along the flat resin surface. Mechanical propertiesof the specimens were evaluated by quasi-static indentation using ananoindenter (Hysitron Tribinderter 900, Minneapolis, Minn., USA) with a100 nm radius cono-spherical diamond tip indenter. A standardtrapezoidal profile was used including a maximum load of 100 mN,indentation hold time of 5 sec, and loading and unloading rates of 20mN/sec. An initial offset load of 10 mN was used for identifying contactand initialize the indentation process. The load-displacement curvesgenerated for the individual indentations were corrected for the offsetforce. Six indentations were performed to characterize the mechanicalbehavior of each SqSH or sol-gel silica control (N=6). Reduced modulusand hardness (in GPa) were calculated based on the Oliver-Pharr methodfor nanoindentation testing (W. C. Oliver, G. M. Pharr, J. Mater. Res.,1992, 7, 1564). Data were analyzed using one-way ANOVA with Tukey'smultiple comparison at α=0.05.

Antimicrobial Activities of Bis-GMA/TEGDMA Resin Containing SqSH

A bis-GMA/TEGDMA light-polymerizable resin blend (composition: 70 weight% bis-GMA, 28.5 weight % TEGDMA, 1 weight % EDMAB and 0.5 weight % CQ)was used to mix with 50 weight % SqSH particles in a centrifugal mixingdevice at 3200 rpm for 60 seconds (DAC 150 Speedmixer; FlackTek Inc.,Landrum, S.C., USA). Bis-GMA/TEGDMA resin without any SqSH was used ascontrol. Polymerization of these resins was achieved by photocuring withvisible light in the wavelength range of 410-500 nm. With a Teflon moldand Mylar sheets covering both sides, polymerized resin disks (6±0.1 mmdiameter, 1 t 0.1 mm thick) were fabricated.

Streptococcus mutans ATCC 35668 (ATCC, Manassas, Va., USA) andActinomyces naeslundii ATCC 12104 were cultured in Brain Heart Infusion(BHI) broth (Difco, Becton-Dickinson and Co., Sparks, Md., USA),supplemented with 50 mM sucrose (pH 7.2). Candida albicans ATCC 90028was cultured in Yeast Nitrogen Base (YNB; Difco) supplemented with 50 mMglucose (pH 7.2). Harvested cells were re-suspended in 100 mL of therespective growth medium, and adjusted to a concentration of 10⁷ CFU/mLbefore use. Each microbe was used individually for the formation ofsingle-species biofilms on salivary pellicle-coated resin disks insidean oral biofilm reactor. After the formation of biofilms on acrylicsurfaces, half of the disks from each group were transferred carefullyinto separate microtubes containing 4 mL of phosphate buffered saline(PBS; 0.01 mM, pH 7.3), avoiding any disturbances to the biofilms. FiftymL of 1 mg/mL solution of2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide(XTT; Sigma-Aldrich) was then added to each microtube, together with 4μL of 1 mM menadione (Sigma-Aldrich). The solutions were mixed gently,covered with aluminum foil, and incubated for 5 hours at 37° C. Afterincubation, the solution was transferred to a new microtube andcentrifuged at 4000 rpm for 10 minutes at 4° C. The supernatant wasplaced in a 96-well plate and read at 492 nm using a spectrophotometer(Victor, R & D systems, Minnesota, USA).

The rest of the disks from each group were placed carefully in separatemicrotubes containing 1 mL of PBS and vortexed (Maxi Mix vortex mixer,Thermo Scientific, Waltham, Mass., USA) for 2 min at high speed todetach the biofilm. Ten-fold serial dilutions were generated in PBS(0.01 mM, pH 7.3), and each dilution was plated (50 μL aliquots) ontoSabouraud Dextrose Agar plates for C. albicans, and Brain Heart Infusionagar plates for S. mutans and A. naeslundii. The plates were incubatedat 37° C. for 48 hours in an aerobic chamber for C. albicans andanaerobic chamber for S. mutans and A. naeslundii. After incubation, thecolony forming counts (CFU) per resin disk were counted manually. Datawere analyzed using one-way ANOVA with Tukey's multiple comparison atα=0.05.

Cytotoxicity

The cytotoxicity of SqSHs and sol-gel silica was investigated using amouse fibroblast cell line (L-929). The growth medium for L-929consisted of Dulbecco's Modified Eagle's Medium (DMEM, Lonza,Wakersville, Md., USA) and 10% fetal bovine serum (Gibco; InvitrogenCorp., Carlsbad, Calif., USA), supplemented with 2 mM L-glutamine, 100U/mL penicillin, and 100 μg/mL streptomycin. The cells were plated in a96-well plate at a density of 5000 cells/cm², in 200 μL of the growthmedium, and incubated at 37° C. in a humidified 5% CO₂ atmosphere. After24 hours, pre-confluent cells were washed twice with serum orantibiotics free DMEM and further incubated in DMEM containing SqSH orsilica particles at different concentrations. Cells incubated in growthmedium without particles were used as the blank control.

The final SqSH or silica dispersions in DMEM were prepared immediatelybefore use by serial dilution (i.e., 2, 5, 25, 125, 625, and 3125 folds)of the stock suspension (ca. 883 μg/mL) with intense vortexing.

Succinic dehydrogenase (SDH) activity of the cells was determined using3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)assay. The retrieved cells were incubated in MTT-succinate solution for60 min and fixed with Tris-formalin. The formazan product was dissolvedin-situ using DMSO and absorbance was recorded using a microplate readerat 562 nm. Results were determined as a percentage of mean controlvalues. The half-maximal inhibitory concentration (IC₅₀) was defined asthe concentration of SqSH or silica particles leading to a 50% reductionin L-929 cell viability A. M. Chen, M. Zhang, D. Wei, D. Stueber, O.Taratula, T. Minko, H. He, Small, 2009, 5, 2673). It was determined bylinear regression analysis of the logarithmic derivative of particleconcentration vs reduction of cell viability using SPSS 16.0 (SPSS Inc.,Chicago, Ill., USA).

Synthesis of SqSH Particles by Hydrolytic Co-Condensation andCharacterization

An issue that confronts silane-based co-condensation reactions ishomocondensation of the trialkoxysilanes (H. Yoshitake, New J. Chem.,2005, 29, 1107). Thus, the reaction products of the sol-gel reactionswere subjected to multiple washings in ethanol prior to analyses toremove unreacted reagents. Attenuated total reflection-Fourier transforminfrared (ATR-FTIR) spectroscopy validates the presence both themethacrylate group at 1690-1714 cm⁻¹ (C═O), 1637 cm⁻¹ (C═C), 1305 cm⁻¹(C—CO—O), 1295 cm⁻¹ (C—CO—O) (S. K. Medda, D. Kundu, G. De, J.Non-Cryst. Solids, 2003, 318, 149), 815 cm⁻¹ (C═C)) and thealkylammonium chain (1373 cm⁻¹ (C—N)(S. Köytepe, T. Seckin, N.Kivrilcim, H. 1. Adigüzel, J. Inorgnomet. Polym., 2008, 18, 222) in thesol-gel reaction products (FIG. 2 e ), thereby confirming theco-condensation of TEOS with 3-MPTS and SIQAC in the multiple-rinsedreaction products.

Using ²⁹Si cross polarization-magic angle spinning nuclear magneticresonance spectroscopy (CP-MAS NMR), two different units were delineatedfrom the NMR spectrum, providing information on the connectivity of thesilica network (C. Bonhomme, C. Coelho, N. Baccile, C. Gervais, T.Azaïs, F. Babonneau, Acc. Chem. Res., 2007, 40, 738):T_(n):RSKOH)_((3−n))(OSi)_(n), and Q_(n):Si(OH)_((4−n))(OSi)_(n) (FIG. 2a ). As shown by the overlay of the NMR spectra of SqSHs and inorganicsol-gel silica synthesized by the Stöber method, with all spectranormalized to the Q₃ unit, the relative areas of the T unit regionincrease linearly as a function of the feed ratio of trialkoxysilanes(3-MPTS and SiQAC) to TEOS (FIGS. 2 b and 2 c ). The degree ofcondensation of Q or T units, as determined by the ratios of therelative areas for different Q or T silicon connections (K. H. Wu, T. C.Chang, C. C. Yang, G. P. Wang, Thin Solid Films, 2006, 513, 84),improves with increased concentration of trialkoxysilane (3-MPTS orSiQAC) in the SqSHs (FIG. 2 d ). This is in agreement with the ATR-FTIRresults (FIG. 2 e ), wherein cyclic Si—O—Si (˜1080 cm⁻¹) (Q. Deng, B.Moore, K. A. Mauritz, Chem. Mater., 1995, 7, 2259) is apparent only inSqSH 1:1:1 and SqSH 1:2:1, both containing high organic components inthe organosilica hybrids. Interestingly, while T₃ (fully-condensedtrimeric species) dominates in the T units, all SqSHs as well as sol-gelsilica present a large amount of Q₃ species bearing one hydroxyl group.This may be explained by the reasoning that hydrolyzed TEOS bearing fourhydroxyl groups has more steric hindrance during condensation, comparedwith trialkoxysilanes with three hydroxyl groups. Thermogravimetricanalysis (TGA) was performed to further characterize the synthesizedSqSHs (FIG. 5 a-c ). The post-calcination residual inorganic massincreases with increasing feed ratios of TEOS to the trialkoxysilanes(3-MPTS and SiQAC), which is consistent with the ²⁹Si NMR results.

By changing the feed ratios of TEOS to the trialkoxysilanes, orderedstructures with variable d spacing within the spherical particles couldbe discerned by XRD and electron microscopy. The SiQAC molecule containsa long hydrophobic alkyl chain linked to the silicon atom by a Si—Cbond, which is chemically stable under hydrolytic conditions. It becomesamphiphilic when silanol groups are formed during hydrolysis (A.Shimojima, K. Kuroda, Chem. Rec., 2006, 6, 53). Based on thisamphiphilic assembly mechanism, lamellar mesostructures may be producedinside the hybrid silica particles within two hours using the Stöberroute with a strong base (ammonium hydroxide) as catalyst. Small anglepowder X-ray diffraction (XRD) patterns of the SqSH 1-n-1 hybrids (n=2,8, 16, and 32) show diffraction peaks corresponding to the d spacingvalue of 2.9±0.1 nm (FIG. 3 ). One should note that these d values aresmaller than that identified from condensed alkysiloxanes with bilayerlamellar structure (d=5.3 nm) A. Shimojima, Y. Sugahara, K. Kuroda,Bull. Chem. Soc. Jpn., 1997, 70, 2847), indicating a different molecularpacking profile. Diffraction peak intensity becomes higher with theincreased ratio of TEOS to SiQAC for SgSH 1-n-1 where n≤8. This impliesthat addition of increased concentrations of TEOS with strongthree-dimensional network formation ability, leads to morehighly-ordered siloxane networks with reduced mesoporosity.Incorporation of tetraalkoxysilane in the self-assembly process ofalkyltrialkoxysilane also contributes to increasing the thermalstability, a feature that could not be attained by hydrolysis andcondensation of alkyltrialkoxysilane alone (A. Shimojima, K. Kuroda,Langmuir, 2002, 18, 1144). The network-forming ability of TEOS was alsoverified by the observation that no particles were formed fromhydrolytic co-condensation of the two trialkoxysilanes (SiQAC and3-MPTS) in the absence of TEOS, under the present experimentalconditions.

Sol-gel silica particles synthesized by the hydrolysis and condensationreactions of TEOS alone in the present study are monodisperse (˜200 nmin diameter; data not shown), whereas the SqSH particles are slightlylarger (ca. 250-1000 nm), and polydisperse, as revealed by scanningelectron microscopy (SEM) (FIG. 4 a ). The SgSH particles exhibited atendency to partially coalesce prior to solidification intoparticulates, producing peanut-like structures (FIG. 6 ). The morphologyof these partially-coalesced SqSH particles is similar to the morphologyof previously-reported particles prepared from the co-condensation ofTEOS with aminopropyltriethoxysilane (APTES) via a Stöber-like route (S.Chen, S. Hayakawa, Y. Shirosaka, E. Fujii, K. Kawabata, K. Tsuru, A.Osaka, J. Am. Ceram. Soc., 2009, 92, 2074). Unlike the TEOS-derivedspherical silica particles which have smooth surfaces, the surfaces ofthe SqSH particles are rough, as observed using transmission electronmicroscopy (TEM), with small aggregates forming around the SqSH particleeven after multiple ethanol rinses (FIG. 4 b ). These surface aggregatesare possibly caused by self-condensation of SiQAC or 3-MPTS that arecovalently bonded to the SqSH surface, as they were resistant to ethanolrinsing and sonication, and became sparser after calcination (FIG. 4 c). For SqSH 1-n-1 (n 8), lamellar structures can be discerned by TEM athigh magnification (FIG. 4 d ). For SqSH 1-n-1 (n>8) lamellar structurescannot be identified by TEM (F FIG. 4 e ); the SqSH particles becamesolid spheres after calcination (FIG. 4 f ).

The presence of silicon, oxygen, nitrogen, carbon within SqSH 1:8:1 andSqSH 1:32:1 particles was confirmed using scanning transmission electronmicroscopy-energy dispersed X-ray analysis (STEM-EDX; FIG. 9 a and FIG.9 b , respectively). Identification of nitrogen within the SqSHparticles is indicative of the presence of the quaternary ammoniumfunctionality (derived from SiQAC) within the entire particle. This iscontrary to a grafting procedure in which the quaternary ammoniumfunctionality is only present along the particle surface. The STEM-EDXdata, however, does not permit conclusions to be drawn with respect tothe methacryloxy functionality derived from 3-MPTS.

Mechanical Properties of SqSH Particles

Silsesquioxane-silica hybrids with different organic/inorganiccompositions and variable structures should be modifiable in terms ofmechanical and biological properties. The mechanical properties of SqSHscan be tuned by altering the TEOS molar feed ratio, so that particleswith higher silica content can be produced. Nanoindentation performed onSqSH particles and sol-gel silica using the method reported by Oliverand Pharr (W. C. Oliver, G. M. Pharr, J. Mater. Res., 1992, 7, 1564)revealed correlations between increases in reduced modulus and hardness,with increasing feed ratios of TEOS to the trialkoxysilane (FIGS. 7 a-7d ).

Antimicrobial Activities of SqSH Incorporated Bis-GMA/TEGDMA Resins

Because SqSHs bearing methacryloxy functional groups can beco-polymerized with methacrylate resin in the presence of certaincatalysts (e.g. photoinitiator and tertiary amine accelerator), SqSHswith different TEOS-trialkoxysilanes molar feed ratios are added into aresin blend consisting of2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) andtriethylene glycol dimethacrylate (TEGDMA), with camphorquinone (CO) andethyl(4-dimethylamino)benzoate (EDMAB) as the photoinitiator andaccelerator, respectively. Incorporation of the SqSH organic-inorganichybrid particles into the methacrylate resin blend results in a seriesof antimicrobial resin composites that may be used for restoring teethand preventing recurrent decay caused by colonization of bacterialbiofilms around the margins of the tooth fillings. Three SqSH-containingresin composites (SqSH 1:8:1, 1:16:1 and 1:32:1) were chosen in thepresent study due to their relatively high reduced modulus and hardness,when compared to sol-gel silica, which are desirable properties forpreparing restorative resin composites. Previous studies havedemonstrated that incorporation of SiQAC-derived sol-gel reactionproducts confers resinous materials with antimicrobial activitiesagainst bacteria and fungi (S.-q.Gong, L.-n. Niu, Kemp L. K., C. K. Y.Yiu, H. Ryou, Y.-p. Qi, J. D. Blizzard, S. Nikonov, M. G. Brakkett, R.L. W. Messer, C. D. Wu, J. Mao, L. B. Brister, F. A. Rueggeberg, D. D.Arola, D. H. Pashley, F. R. Tay, Acta Biomater., 2012, 8, 3270; S. Q.Gong, J. Epasinghe, F. A. Rueggeberg, L. N. Niu, D. Mettenberg, C. K. Y.Yiu, J. D. Blizzard, C. D. Wu, J. Mao, C. L. Drisko, D. H. Pashley, F.R. Tay, PLoS One, 2012, 7, e42355; S. Q. Gong, D. J. Epasinghe, B. Zhou,L. N. Niu, K. A. Kimmerling, F. A. Rueggeberg, C. K. Y. Yiu, J. Mao, D.H. Pashley, F. R. Tay, Acta Biomater., 2013, 9, 6964). The antimicrobialpotentials of SqSH-containing methacrylate resins against Streptococcusmutans, Actinomyces naeslundii, and Candida albicans were confirmedusing2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide(XTT) and Colony Forming Unit (CFU) assays (FIGS. 8 a-c ). Streptococcusmutans and A. naeslundii are cariogenic oral pathogens, while C.albicans is associated with oral candidiasis in susceptible hosts. It islikely that the antimicrobial activities of SqSH containing methacrylateresins are permanent and non-leaching (S. Q. Gong, J. Epasinghe, F. A.Rueggeberg, L. N. Niu, D. Mettenberg, C. K. Y. Yiu, J. D. Blizzard, C.D. Wu, J. Mao, C. L. Drisko, D. H. Pashley, F. R. Tay, PLoS One, 2012,7, e42355; S. Q. Gong, D. J. Epasinghe, B. Zhou, L. N. Niu, K. A.Kimmerling, F. A. Rueggeberg, C. K. Y. Yiu, J. Mao, D. H. Pashley, F. R.Tay, Acta Biomater., 2013, 9, 6964), as SqSH particles areco-polymerized with the methacrylate network. This non-leachingantimicrobial activity is independent of the loss of surface layer ofthe composite by wear during function, since SqSH particle are dispersedthroughout the bulk resin matrix.

Because materials that possess antimicrobial properties against bacteriaor fungi may be toxic to mammalian cells, we performed3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assayon a mouse fibroblast cell line (L929) to examine the effects ofincreasing molar feed ratios of SIQAC on the cytotoxicity of SqSHs(FIGS. 10 a-b ). The results demonstrate a significant positivecorrelation between the 50% reduction in cell viability (IC₅₀) of themammalian cells and the molar feed ratio of TEOS employed for thesynthesis of the SqSH particles.

Mesoporous antimicrobial SqSH particles with spherical morphology andlamellar structures may also be used as absorbents or carriers forloading bioactive agents, such as growth factors, catalysts, metal ions,and photoactive molecules, to achieve other functions. Otheralkoxysilanes with different organofunctional moieties (e.g., acrylate,methacrylate, (C₂-C₈)alkenyl, glycidyloxy, epoxy, sulfonate,carboxylate, ester, amino, acrylamide, methacrylamide, isocyanato, aminoacid, nucleic acid, mercapto(C₁-C₆)alkyl, and the like) may be used inlieu of 3-MPTS, enabling these hybrid particles to satisfy differentproduct requirements. The versatile functionality of these hybridmaterials will expand the range of their applications in various fields.For example, antimicrobial SqSH particles containing acrylatefunctionalities may be incorporated into acrylate-based paints;antimicrobial SqSH particles containing vinyl functionalities may beblended with polypropylene via an extruder to produce antimicrobial foodwraps for the food industry.

CONCLUSIONS

A facile method has been developed for synthesizing unique SqSH hybridsilica particles via a Stöber-like approach, with ordered lamellarstructures with spherical morphology, without the use of additionalsurfactants. The one-pot synthesis approach leads to the development ofunique and useful antimicrobial hybrid silica particles with quaternaryammonium groups distributed within the entire particles, and therefore,non-leaching antimicrobial activities, as opposed to a graftingprocedure, where thus type of functionality is present only along theparticle surface. Moreover, antimicrobial activities are presentirrespective of the degree of mesoscopic order of the hybrid silicaparticles. This synthesis approach may be further expanded by replacingthe curing functionality with other organofunctional moieties, therebyenabling the antimicrobial hybrid particles with tunable mechanicalproperties to be incorporated into different polymers/copolymers for awide range of commercial applications. Likewise, this synthesis approachmay be further expanded by replacing the antimicrobial functionalitywith other organofunctional moieties, thereby enabling the antimicrobialhybrid particles with tunable biological properties to be incorporatedinto different polymers/copolymers for a wide range of commercialapplications.

When ranges are used herein for physical properties, such as molecularweight, or chemical properties, such as chemical formulae, allcombinations, and subcombinations of ranges specific embodiments thereinare intended to be included.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in their entirety.

Those skilled in the art will appreciate that numerous changes andmodifications can be made to the preferred embodiments of the inventionand that such changes and modifications can be made without departingfrom the spirit of the invention. It is, therefore, intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A tooth desensitizer, comprising a solutioncomprising at least one filling material selected from the groupconsisting of siloxanes, glass ionomers, methacrylates, and silveramalgams; and a silsesquioxane-silica hybrid, wherein thesilsesquioxane-silica hybrid comprises: a silica particle covalentlybound to: (1) a residue having the formula: wherein:

R^(c) is (C₁₋₂)alkyl; R^(d) is (C₁₋₂)alkyl or phenyl; R^(c) is(C₆₋₂₂)alkyl; X⁻ is an anion selected from the group consisting ofchloride, bromide, fluoride, iodide, sulfonate, and acetate; and (2) aresidue comprising a curing group selected from the group consisting ofacrylate, methacrylate, (C₂-C₈)alkenyl, glycidyloxy, epoxy, sulfonate,carboxylate, ester, amino, acrylamide, methacrylamide, isocyanato, aminoacid, nucleic acid, mercapto(C₁-C₆)alkyl, and combinations thereof,wherein the solution is a water solution or a water-alcohol solution. 2.The tooth desensitizer of claim 1, wherein the curing group selectedfrom the group consisting of acrylate, methacrylate, (C₂-C₈)alkenyl,acrylamide, methacrylamide, and combinations thereof.
 3. The toothdesensitizer of claim 1, the curing group is methacrylate.
 4. The toothdesensitizer of claim 1, the curing group is methacryloxypropyl.
 5. Thetooth desensitizer of claim 1, wherein R^(c) is methyl.
 6. The toothdesensitizer of claim 1, wherein R^(d) is methyl.
 7. The toothdesensitizer of claim 1, wherein R^(e) is octadecyl.
 8. The toothdesensitizer according to claim 1, further comprising at least oneco-monomer is selected from the group consisting of (C₂-C₈) alkene,vinyl chloride, acrylate, methacrylate, acrylamide, methacrylamide, andcombinations thereof.
 9. A kit, comprising: (a) a plurality ofsilsesquioxane-silica hybrid particles, wherein thesilsesquioxane-silica hybrid particles comprises: silica covalentlybound to: (1) a residue having the formula:

wherein: R^(c) is (C₁₋₂)alkyl; R^(d) is (C₁₋₂)alkyl or phenyl; R^(c) is(C₆₋₂₂)alkyl; X⁻ is an anion selected from the group consisting ofchloride, bromide, fluoride, iodide, sulfonate, and acetate; and (2) aresidue comprising a curing group selected from the group consisting ofacrylate, methacrylate, (C₂-C₈)alkenyl, glycidyloxy, epoxy, sulfonate,carboxylate, ester, amino, acrylamide, methacrylamide, isocyanato, aminoacid, nucleic acid, mercapto(C₁-C₆)alkyl, and combinations thereof; and(b) at least one polymerization initiator, wherein the kit furthercomprises a natural rubber, a synthetic rubber, a thermoplastic polymer,or a combination thereof.
 10. The kit according to claim 9, furthercomprising at least one synergist, at least one filler, or at least oneco-monomer.
 11. The kit according to claim 10, further comprising atleast one co-monomer selected from the group consisting of (C₂-C₈)alkene, vinyl chloride, acrylate, methacrylate, acrylamide,methacrylamide, and combinations thereof.
 12. The kit according to claim11, wherein said co-monomer is selected from the group consisting ofmethyl methacrylate, ethylene, propylene, hydroxyethyl methacrylate, 1,6-hexanediol dimethacrylate, bisphenol A-glycidyl methacrylate(bis-GMA), triethylene glycol dimethacrylate (TEGMA), urethanedimethacrylate, and combinations thereof.
 13. The kit according to claim9, wherein said plurality of particles has an average particle size ofabout 50 nm to about 2000 nm.
 14. The kit according to claim 9, whereinsaid plurality of particles has a polydispersity index (PDI=M_(w)/M_(n))of about 1 to about
 20. 15. The kit according to claim 9, wherein thekit further comprises a natural rubber, a synthetic rubber, or acombination thereof.
 16. The kit according to claim 9, wherein the kitfurther comprises a thermoplastic polymer.